The present invention relates to a hose rupture control valve unit (holding valve), which is provided in a hydraulic machine, such as a hydraulic excavator, for preventing a drop of a load upon rupture of a cylinder hose.
In a hydraulic machine, e.g., a hydraulic excavator, there is a need for preventing a drop of a load even if a hose or steel pipe for supplying a hydraulic fluid to a hydraulic cylinder, i.e., an actuator for driving the load such as a boom, should be ruptured. To meet such a need, a hose rupture control valve unit, also called a holding valve, is provided in the hydraulic machine. One of conventional hose rupture control valve units is disclosed in, e.g., JP,A 11-303810. FIG. 6 shows a hydraulic circuit diagram of the conventional valve unit.
Referring to FIG. 6, numeral 100 denotes a conventional hose rupture control valve unit. The valve unit 100 comprises a housing 3 provided with two input/output ports 1, 2. The input/output port 1 is directly attached to a bottom port 102a of a hydraulic cylinder 102, and the input/output port 2 is connected to one of actuator ports of a control valve 103 via an actuator line 105. Within the housing 3, there are provided a poppet valve member 55 serving as a main valve, a spool valve member 60 operated by a pilot pressure supplied as an external signal from a manual pilot valve 108 and operating the poppet valve member 55, and a small relief valve 7. A throttle 34 serving as pressure generating means is provided in a drain passage 15d of the small relief valve 7. The spool valve member 60 is of a structure having one pressure bearing chamber 17 to which the pilot pressure (external signal) is introduced, and also having another pressure bearing chamber 35 provided on the same side as the pressure bearing chamber 17 in series. The upstream side of the throttle 34 is connected to the pressure bearing chamber 35 via a signal line 36 so that the pressure generated by the throttle 34 acts upon the spool valve member 60 to provide a driving force on the same side as that provided by the pilot pressure, i.e., the external signal.
In the normal state where the actuator line 105 is not ruptured, the hose rupture control valve unit 100 operates as follows.
When supplying a hydraulic fluid to the bottom side of the hydraulic cylinder 102, a control lever of the manual pilot valve 108 is operated in a direction indicated by A for switching over the control valve 103 to its right shift position as viewed in the drawing. With the switchover of the control valve 103, the hydraulic fluid is supplied from a hydraulic pump 101 to a hose connection chamber 9 of the valve unit 100 via the control valve 103 and the pilot line 105, whereupon the pressure in the hose connection chamber 9 rises. At this time, the pressure in a cylinder connection chamber 8 of the valve unit 100 is equal to the load pressure on the bottom side of the hydraulic cylinder 102. Therefore, when the pressure in the hose connection chamber 9 becomes higher than the load pressure, the poppet valve member 55 moves upward in the drawing and the hydraulic fluid flows into the cylinder connection chamber 8, whereby the hydraulic fluid is supplied from the hydraulic pump 101 to the bottom side of the hydraulic cylinder 102.
When draining the hydraulic fluid from the bottom side of the hydraulic cylinder 102 to the control valve 103, the control lever of the manual pilot valve 108 is operated in a direction indicated by B for switching over the control valve 103 to its left shift position as viewed in the drawing. With the switchover of the control valve 103, the hydraulic fluid is supplied from the hydraulic pump 101 to the rod side of the hydraulic cylinder 102 via the control valve 103 and a pilot line 106. At the same time, the pilot pressure from the manual pilot valve 108 is introduced to the pressure bearing chamber 17 of the spool valve member 60, causing the spool valve member 60 to open by the pilot pressure. This forms a pilot flow streaming from the cylinder connection chamber 8 to the actuator line 105 via a feedback slit 11, a pilot passage 15a, a variable throttle portion 60a, and a pilot passage 15b. The pressure in a back pressure chamber 10 lowers under the action of the variable throttle portion 60a and the feedback slit 11, whereby the poppet valve member 55 is opened at an opening degree in proportion to the opening degree of the variable throttle portion 60a. Accordingly, the hydraulic fluid on the bottom side of the hydraulic cylinder 102 is drained to the control valve 103 while the flow rate is controlled, and then drained to a reservoir 109.
In the condition where the load pressure on the bottom side of the hydraulic cylinder 102 becomes high, such as encountered when holding a suspended load with the control valve 103 maintained in a neutral position, the poppet valve member 55 in its cutoff position holds the load pressure and fulfills the function of reducing the amount of leakage (i.e., the function of a holding valve) similarly to a conventional holding valve.
When an excessive external force acts upon the hydraulic cylinder 102 and the pressure in the cylinder connection chamber 8 is increased, the pressure on the input side of the small relief valve 7 rises, whereupon the small relief valve 7 is opened and the hydraulic fluid flows into the drain passage 15d, in which the throttle 34 is provided. This raises the pressure in the signal passage 36 and opens the spool valve member 60, thereby forming a pilot flow that streams from the cylinder connection chamber 8 to the actuator line 105 via the feedback slit 11, the back pressure chamber 10, and the pilot passages 15a, 15b. Accordingly, the poppet valve member 55 is opened and the hydraulic fluid at an increased pressure produced upon exertion of an external force is drained to the reservoir 109 through an overload relief valve 107a, which is connected to the actuator line 105. As a result, equipment breakage can be prevented.
In the event of rupture of the actuator line 105, the following problem occurs in point of safety if the hose rupture control valve unit 100 is not provided. When the hydraulic cylinder 102 is, e.g., a boom cylinder for moving a boom of a hydraulic excavator up and down, the hydraulic fluid on the bottom side of the hydraulic cylinder 102 flows out from the ruptured actuator line 105, thus causing a drop of the boom. The hose rupture control valve unit 100 serves to ensure safety in such an event. More specifically, as with the case of holding a suspended load as mentioned above, the poppet valve member 55 in the cutoff position functions as a holding valve to prevent outflow of the hydraulic fluid from the bottom side of the hydraulic cylinder 102, whereby a drop of the boom is prevented. Also, when lowering the boom down to a safety position from the condition where the boom is held in midair, the control lever of the manual pilot valve 108 is operated in the direction indicated by B, whereupon the pilot pressure from the manual pilot valve 108 is introduced to the pressure bearing chamber 17 of the spool valve member 60. The spool valve member 60 is opened by the pilot pressure, and hence the poppet valve member 55 is also opened. As a result, the hydraulic fluid on the bottom side of the hydraulic cylinder 102 can be drained while the flow rate of the drained hydraulic fluid is controlled, allowing the boom to be slowly lowered.
However, the above-described prior art has the problem as follows.
In the conventional hose rupture control valve unit shown in FIG. 6, when the hydraulic cylinder 102 is, e.g., the boom cylinder for moving the boom of the hydraulic excavator up and down as mentioned above, the control lever of the manual pilot valve 108 is sometimes abruptly reversed from the shift position in the direction B to the opposite shift position in the direction A, as viewed in the drawing, for quickly changing the operating direction of the boom from the downward to the upward. With such an abrupt reversed operation of the control valve, the boom-raising pilot pressure generated upon the control lever being operated in the direction A rises for switching over the control valve 103 to the right shift position in the drawing before the boom-lowering pilot pressure generated upon the control lever being operated in the direction B lowers down to a level lower than the valve-opening pressure of the spool valve member 60. This causes a main flow rate to be introduced to the hose connection chamber 9 of the hose rupture control valve unit 100 through the actuator line 105 before the spool valve member 60 is closed. Therefore, the boom-raising thrust pressure induced by the main flow rate is introduced to the hose connection chamber 9 of the hose rupture control valve unit 100, and at the same time a part of the main flow rate is introduced to the back pressure chamber 10 of the poppet valve member 55 via the pilot passages 15b, 15a. Opening of the poppet valve member 55 is thereby impeded and delayed. As a result, when the operation is abruptly reversed from the mode of raising the boom to the mode of lowering it, the startup of the boom-raising operation is delayed and the smooth operation cannot be obtained. A similar problem also occurs when the member driven by the hydraulic cylinder 102 is other than the boom.
An object of the present invention is to provide a hose rupture control valve unit which comprises a main valve constituted by a poppet valve member and a pilot valve constituted by a spool valve member and controlling the operation of the main valve, and in which a hydraulic fluid can be supplied from a hose connection chamber to a cylinder connection chamber even in the condition of a pilot pressure acting upon the spool valve member, so that the smooth operation can be obtained without a delay in opening of the poppet valve member upon an abrupt reversed lever operation.
(1) To achieve the above object, the present invention provides a hose rupture control valve unit comprising a poppet valve member slidably disposed within a housing between a supply/drain port of a hydraulic cylinder and a hydraulic hose, the housing being provided with a cylinder connection chamber connected to the supply/drain port, a hose connection chamber connected to the hydraulic hose, and a back pressure chamber, the poppet valve member serving as a main valve for selectively cutting off and establishing communication between the cylinder connection chamber and the hose connection chamber; and a spool valve member disposed in pilot passages connecting the back pressure chamber and the hose connection chamber, and operated by the external signal to selectively cut off and establish communication through the pilot passages, the poppet valve member having throttle passages for communicating the cylinder connection chamber and the back pressure chamber with each other, wherein the hose rupture control valve unit further comprises pressure control means for preventing a pressure from being generated in the back pressure chamber to such an extent as impeding opening of the poppet valve member when a hydraulic fluid is introduced from the hydraulic hose to the hose connection chamber before the spool valve member is closed.
By providing the pressure control means for preventing a pressure from being generated in the back pressure chamber to such an extent as impeding opening of the poppet valve member when a hydraulic fluid is introduced from the hydraulic hose to the hose connection chamber before the spool valve member is closed, the hydraulic fluid can be supplied from the hose connection chamber to the cylinder connection chamber even in the condition of a pilot pressure acting upon the spool valve member. As a result, the smooth operation can be obtained without a delay in opening of the poppet valve member upon an abrupt reversed lever operation.
(2) In above (1), preferably, the pressure control means is a check valve disposed in the pilot passage and cutting off a flow of the hydraulic fluid from the hose connection chamber to the back pressure chamber.
With that feature, even when the hydraulic fluid is introduced from the hydraulic hose to the hose connection chamber before the spool valve member is closed, the pressure of the hydraulic fluid in the hose connection chamber is not transmitted to the back pressure chamber. It is therefore possible to prevent a pressure from being generated in the back pressure chamber to such an extent as impeding opening of the poppet valve member.
(3) Also, in above (1), preferably, the pressure control means comprises a check valve provided inside the poppet valve member and allowing a flow of the hydraulic fluid from the back pressure chamber to the cylinder connection chamber, and means disposed in the pilot passage and generating a differential pressure between the hose connection chamber and the back pressure chamber.
With that feature, even if the hydraulic fluid is supplied from the hose connection chamber to the back pressure chamber when the hydraulic fluid is introduced from the hydraulic hose to the hose connection chamber before the spool valve member is closed, the hydraulic fluid is allowed to pass through the check valve and a pressure is prevented from accumulating in the back pressure chamber. Also, since a differential pressure occurs between the hose connection chamber and the back pressure chamber so that the pressure in the back pressure chamber lowers, it is therefore possible to prevent a pressure from being generated in the back pressure chamber to such an extent as impeding opening of the poppet valve member.